exception unhandled

Question

           

string cellvalue = dataGridView1["customer_id", index].Value.ToString();
 SqlCommand cmdd = new SqlCommand("SELECT * FROM bike_sales  WHERE customer_id='" + cellvalue + "'", my);
            SqlDataReader rdd = cmd.ExecuteReader();
            rdd.Read();
            up.textBox26.Text = rdd["stock_id"].ToString();,,,,,,,,,,,,,,,,,,,,,,here i got error index out of range exception unhandled
whats wrong with it hlp plz